This invention relates to the field of automated data storage systems, and in particular to carousel data library systems in which many discrete media elements, such as tape cartridges, are stored and manipulated for access to the information recorded therein.
Tape cartridge libraries are in demand as a means of providing relatively rapid and automatic access to a large quantity of information at low cost, while also providing conveniently compact storage. One example of a prior art cartridge library is the IGM-ATL 2300 automated tape library, sold by IGM Data AutoLoader Division, based in Bellingham, Wash. That system used a carousel to carry up to fifty-four 8 mm tape cartridges, for automatic loading into tape drives, with access to a total storage volume of up to 270 gigabytes of data. Another example prior art system is the STL-8000 8 mm automated tape library, offered by Spectra Logic of Boulder, Colo., using a carousel with space for forty cartridges.
Such prior art systems were not without disadvantages. For example, the weight of the carousel was often excessive for easy handling by human operators. In addition, the schemes employed for retaining cartridges within the carousel sometimes proved unsatisfactory in use. In the case of the ATL-2300, for instance, the carousel had one configuration for transport and handling, and another for use. In the "secure" mode for handling, each cartridge was constrained from radial motion out of the carousel by a metal peg protruding downward from the carousel top at the outer edge, aligned roughly at the middle of the cartridge chamber. When installed in the library, the carousel was manually shifted to the operating configuration by rotation of a knob, which angularly displaced the set of fifty-four pegs so that they were no longer aligned with the chambers, thus permitting the cartridges to move in and out.
If the carousel were removed from the library without first securing the cartridges, the cartridges could slide and fall out of the carousel unintentionally. Furthermore, in operating configuration within the library, the cartridges were not constrained from migrating outward as a result of vibration and frequent acceleration of the carousel, bringing a risk of jamming of the mechanism. The manually operated peg system also added undesired weight to the carousel; the weight of the tape cartridges is significant in itself, and additional structural weight is undesirable.
The configuration of the library also yielded inefficiencies. For example, the ATL-2300 cartridges were carried radially in the carousel, and need to be pushed into and out of the carousel for use by tape drives placed outside the carousel. Motorized pushing shafts were placed near the axis of the carousel to push the cartridges outward toward the tape drives, but separate systems, located outside the carousel by the tape drives, were needed to push them back in again. Additional complexity and costs arise from the extra motors, shafts, and so forth needed for the separate pushing operations.
In the case of the STL-8000, the tape drives were placed entirely within the inner diameter of the carousel. This required placement of each cartridge at an angle to the carousel, rather than radially, and restricted the number of cartridges that could be carried while still fitting within the form factor required for standard cabinet racks. Reduced storage capacity was a result. In addition, placement of the tape drives in the interior of the carousel increases the difficulty of providing cooling air to the drives.
Consequently, a need exists for a carousel library system having a lightweight carousel that has a simple and automatic scheme for retaining cartridges securely during transport and handling, and retaining them in place during motion of the carousel, but permitting easy removal by the library mechanism when desired. An ideal system would also have provisions for moving cartridges back and forth from tape drives to the carousel that is simple and robust while employing fewer motors and related hardware. It is also highly desirable to minimize the chance that cartridges will be improperly loaded into the carousel, and to provide a convenient way for individual cartridges to be added to or withdrawn from the carousel without removing the carousel from the library.
Achieving each of these desired attributes is complicated by the choice of media. For standard 8 mm data cartridges, the design of the cartridge case offers few features to be exploited for easy handling or for ensuring proper orientation.